Since you raked out most of the pea gravel that'll allow them to scratch into the dirt a little and find the grit they need too. They'll like that. Should be easy to rinse out if it does get stinky too. Chickens like to take dust baths to stay clean and help keep mites and other micro pests away. My run is clay based "dirt" that gets really hard so I gave them a large tote with slightly coarse builders sand and they all use it about once a day. They're fun to watch too. Just put a few drain holes in the tote or under a covered area to keep the sand dry.
I think you've got it going but I agree that the bigger the run the happier they'll be.